The present invention relates to laminated resinoid wheels for cutting hard metal materials, a method for continuously producing the resinoid wheels and an apparatus to be used for the method.
Generally, the cutting ability of resinoid wheel varies with the kind of abrasive grains, grain size, kind of binder and porosity. Grinding wheels of various hardnesses have heretofore been produced from a single composition, and a wheel of particular hardness is selected for use in accordance with the material and construction of the articles to be cut. Thus a hard grinding wheel is used for cutting hard metal materials. However, the harder the grinding wheel, the greater will be the cutting resistance encountered, with the result that cutting operation produces a large amount of heat which scorches the cut surface of the material, causing distortion, changes in the hardness of the cut portion and discoloration in the cut surface. Moreover, the irregularities left over along the periphery of cut portion need further finishing procedure. In addition, it is difficult to provide a planar cut surface with a sharp cut edge, whilst the rough abrasive surface is liable to be clogged up to render the wheel no longer operative.
Conventional resinoid wheels have been produced by placing a kneaded resinoid abrasive composition into a die of a given shape, smoothing the surface of the composition with raking means to give a uniform thickness to the mass of the composition, molding the composition at an elevated pressure and baking the molded product. However, this method has the drawback that relatively coarse abrasive grains are caught by the raking means and brought to the surface, rendering the resulting product uneven in grain size distribution. Further according to the conventional method, the raked mass of the starting abrasive composition is pressed on one side for molding. Consequently, the grinding wheel obtained becomes uneven in hardness, inasmuch as the product has high hardness where many coarse abrasive grains are present but low hardness where smaller grains are predominant. When put to use, the grinding wheel wears away more markedly where it contains many fine abrasive grains than where coarse grains predominate, so that an uneven wear takes place. As a result, the grinding wheel not only fails to cut a work straight but is also subjected to an objectionable force and possibly broken in an extreme case. Moreover, if the abrasive composition is not fully raked, the resulting product will have a nonuniform thickness, consequently producing errors when cutting a hard metal material, and a markedly irregular portion of the grinding wheel, if any, will cause an objectionable force to act on and break the grinding wheel during use.